8 Years
May 14, 2011
Smoky Mountains
You know, if I had tried doing all this 20 years ago, I'd be able to read it once and I'd know it. After sitting here for hours reading tons of threads, I basically feel like I'm experiencing advanced Alzheimers.

So, I'm candling early. I set them Monday. Hey, it's tough to hold out. So out of 8 eggs, I found 2 definite embryos with spider veins. 1 was dropped and frankly I have no idea what the hell I was looking at with that one. As for the rest, all but maybe 1 seemed to show a very well defined air sac. The question I had, and that was probably answered in at least 74 threads I read, is...does air sac mean development of some kind? Or will there be an air sac after a period of time even after sitting on my counter waiting to be fried? I'm not looking at tossing anything yet, it's too early, and it's my first time. So I'll wait. But other than the obvious spidering and embryo, is the air sac a sign of anything?


8 Years
Feb 19, 2011
Suffolk, UK

All eggs will gradually lose moisture whether they are fertile or not. However once incubation commences then the eggs are subject to conditions that will increase the rate of moisture loss. Once fertile eggs develop then this rate is increased by the embryo's requirement for water. Overall the air cell should increase gradually throughout incubation and becomes more obvious after about 7 days.

Larger air cells on fresh eggs usually mean they've been stored for a longer period or are damaged/porous. Its always useful to candle fresh eggs to assess for age and damage.



10 Years
Jan 11, 2010
The air sac itself does not indicate that an embryo is growing. While being formed the egg and contents are at body temperature- after being laid the eggs cools down causing the interior and membrane to contract slightly. The air cell size can indicate through out incubation if humidity levels are too high or low. By the end - the air cell should take up around 1/3 of the egg allowing the chick enough room and air to hatch successfully.

You may find this interesting- it shows the development each day of a chicken, ( the eggs are broken open- just thought I would warn you in case of a queezey stomach ) sometimes when candling its helpful to know what you should be looking for.


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